System and method for decompensation detection and treatment based on patient hemodynamics

ABSTRACT

A system and method for detecting and treating symptoms of early decompensation utilizing a cardiac rhythm management. The system applies an electrical stimulus to the patient&#39;s heart at a first set of pacing parameters including a lower rate limit (LRL) setting, and acquires a coronary venous pressure (CVP) signal from a pressure sensor implanted in a coronary vein of the patient. An average coronary venous end diastolic pressure (CV-EDP) value is calculated from the CVP signal. The system monitors the average CV-EDP value over a predetermined interval, and dynamically adjusts the LRL setting responsive to the detection of a first or a second predetermined event based on the average CV-EDP value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119 of U.S.Provisional Application No. 61/182,918, filed Jun. 1, 2009, entitled“System and Method for Decompensation Detection and Treatment Based onPatient Hemodynamics,” which is incorporated herein by reference for allpurposes.

This application is also related to co-pending and commonly assignedU.S. Patent Publication No. 2010/0305650, filed on May 26, 2010, andentitled “System and Method for Pacing Rate Control Utilizing PatientHemodynamic Status Information,” which is incorporated herein byreference for all purposes.

TECHNICAL FIELD

The present invention relates to medical devices and methods for cardiacrhythm management. More specifically, the present invention relates tosystems and methods for automatically adjusting the operating parametersof a cardiac pacemaker or cardiac resynchronization therapy system.

BACKGROUND

Implantable cardiac rhythm management (CRM) systems, includingpacemakers, implantable cardioverter/defibrillators (ICDs), and cardiacresynchronization therapy (CRT, CRT-D) devices have been used to delivereffective treatment to patients with serious cardiac arrhythmias. Inparticular, rate adaptive pacing systems are known which utilize dataobtained from various implanted sensors to adjust pacing parameters inresponse to increased patient demand.

SUMMARY

The present invention, in one embodiment, is a method of operating animplanted cardiac rhythm management system in a patient. The methodcomprises applying an electrical stimulus to the patient's heart at afirst set of pacing parameters including a lower rate limit (LRL)setting. The method further comprises acquiring a coronary venouspressure (CVP) signal from a pressure sensor implanted in a coronaryvein of the patient. An average coronary venous end diastolic pressure(CV-EDP) value is calculated from the CVP signal, and the average CV-EDPvalue is monitored over a predetermined interval. The method furthercomprises dynamically adjusting the LRL setting responsive to thedetection of a first or a second predetermined event based on theaverage CV-EDP value.

In another embodiment, the present invention is a method of operating animplanted cardiac rhythm management system in a patient, the methodcomprising applying an electrical stimulus to the patient's heart at afirst set of pacing parameters including an LRL setting, acquiring a CVPsignal from a pressure sensor implanted in a coronary vein of thepatient, and calculating a baseline CV-EDP value from the CVP signalcorresponding to a first interval. The average CV-EDP values aremonitored over a predetermined time interval subsequent to the firstinterval. The method further comprises comparing each of the averageCV-EDP values to the baseline CV-EDP value, and automatically increasingthe LRL setting in response to a difference (ΔCV-EDP) between at leastone of the average CV-EDP values and the baseline average CV-EDP valueexceeding a predetermined threshold. The method further comprisessubsequently automatically reducing the LRL setting upon detecting apredetermined event.

In yet another embodiment, the present invention is an implantable rateadaptive cardiac rhythm management system configured for applying apacing stimuli to a patient's heart, the pacing stimuli defined bypacing parameters including a pacing rate and an LRL setting. The systemcomprises a plurality of implantable medical electrical leads and animplantable pulse generator. The leads are configured to sense cardiacelectrical activity and to deliver the pacing stimuli, at least one ofthe leads being configured for chronic implantation within a coronaryvein of the patient's heart and including a pressure sensor configuredto generate a coronary venous pressure (CVP) signal indicative of fluidpressure within the coronary vein. The pulse generator is operativelycoupled to the leads and is configured to generate the pacing stimuli,and includes a control system configured to acquire the CVP signal fromthe pressure sensor, calculate an average coronary venous end diastolicpressure (CV-EDP) value from the CVP signal, and monitor the calculatedaverage CV-EDP value over a predetermined interval. The control systemis further configured to dynamically adjust the LRL setting responsiveto the detection of a first or a second predetermined event based on thecalculated average CV-EDP value.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an implantable cardiac rhythmmanagement (CRM) system according to one embodiment of the presentinvention in a deployed configuration.

FIG. 2 is a block diagram illustrating functional components of theimplantable medical system of FIG. 1.

FIG. 3 is an illustration of coronary venous system pressure waveformsthat can be obtained utilizing the CRM system of FIG. 1.

FIG. 4 is an illustration depicting a coronary venous pressure waveformand corresponding left ventricular pressure waveform.

FIG. 5 is a diagram illustrating an exemplary method of operating theCRM system of FIG. 1 to treat symptoms associated with CHF according toone embodiment of the present invention.

FIG. 6 is a flow chart illustrating a method of operating the CRM systemof FIG. 1 to treat symptoms associated with CHF according to oneembodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic drawing of an implantable cardiac rhythmmanagement (CRM) system 10 according to one embodiment of the presentinvention, shown in a deployed state. As shown in FIG. 1, the CRM system10 includes a pulse generator 12 coupled to a cardiac lead system 13including a pair of medical electrical leads 14, 16 deployed in apatient's heart 18, which includes a right atrium 20 and a rightventricle 22, a left atrium 24 and a left ventricle 26, a coronary sinusostium 28 in the right atrium 20, a coronary sinus 30, and variouscoronary veins including an exemplary branch vessel 32 off of thecoronary sinus 30.

As discussed in detail below, the CRM system 10 is advantageouslyconfigured to treat cardiac arrhythmias in a patient suffering from CHF.More specifically, the CRM system 10 is configured to adjust pacingparameters to relieve symptoms associated with early decompensationresulting from CHF. The CRM system 10 utilizes hemodynamic performanceinformation based on the output from implanted pressure sensors todiagnose medical conditions, such as the onset of early decompensationresulting from CHF, and to optimize the pacing system parameters totreat CHF-related symptoms. In various embodiments, the pressure sensorsprovide information that is indicative of or correlates closely to thepatient's left ventricular pressure (LVP), which is a useful measure asan indicator of cardiac function in patients suffering from CHF.

As shown in FIG. 1, the lead 14 includes a proximal portion 42 and adistal portion 36, which as shown is guided through the right atrium 20,the coronary sinus ostium 28 and the coronary sinus 30, and into thebranch vessel 32 of the coronary sinus 30. The distal portion 36 furtherincludes pressure sensors 38, 39, and an electrode 40. As shown, thepressure sensor 39 and the electrode 40 are positioned on the lead 14such that, when implanted, they are both located within the branchvessel 32. As further shown, the pressure sensor 38 is positioned on thelead 14 such that, when implanted, it is located within the right atrium20. Alternatively, the additional pressure sensor 38 could be located inthe coronary sinus 30. The illustrated position of the lead 14 may beused for delivering a pacing and/or defibrillation stimulus to the leftside of the heart 18. Additionally, the lead 14 may also be partiallydeployed in other regions of the coronary venous system, such as in thegreat cardiac vein or other branch vessels for providing therapy to theleft side or right side of the heart 18.

In the illustrated embodiment, the electrode 40 is a relatively small,low voltage electrode configured for sensing intrinsic cardiacelectrical rhythms and/or delivering relatively low voltage pacingstimuli to the left ventricle 26 from within the branch coronary vein32. In various embodiments, the lead 14 can include additionalpace/sense electrodes for multi-polar pacing and/or for providingselective pacing site locations.

As further shown, in the illustrated embodiment, the lead 16 includes aproximal portion 34 and a distal portion 44 implanted in the rightventricle 22. In other embodiments, the CRM system 10 may include stilladditional leads, e.g., a lead implanted in the right atrium 20. Thedistal portion 44 further includes a flexible, high voltage electrode46, a relatively low-voltage ring electrode 48, and a low voltage tipelectrode 50 all implanted in the right ventricle 22 in the illustratedembodiment. The high voltage electrode 46 has a relatively large surfacearea compared to the ring electrode 48 and the tip electrode 50, and isthus configured for delivering relatively high voltage electricalstimulus to the cardiac tissue for defibrillation/cardioversion therapy,while the ring and tip electrodes 48, 50 are configured as relativelylow voltage pace/sense electrodes. The electrodes 48, 50 provide thelead 16 with bi-polar pace/sense capabilities.

In various embodiments, the lead 16 includes additionaldefibrillation/cardioversion and/or additional pace/sense electrodespositioned along the lead 16 so as to provide multi-polardefibrillation/cardioversion capabilities. In one exemplary embodiment,the lead 16 includes a proximal high voltage electrode in addition tothe electrode 46 positioned along the lead 16 such that it is located inthe right atrium 20 (and/or superior vena cava) when implanted.Additional electrode configurations can be utilized with the lead 16. Inshort, any electrode configuration can be employed in the lead 16without departing from the intended scope of the present invention.

In various embodiments, the lead 14 can be configured according to thevarious embodiments described in co-pending and commonly assigned U.S.Provisional Patent Application 61/088,270 titled “Implantable Lead andCoronary Venous Pressure Sensor Apparatus and Method” to Liu, et al. orcommonly assigned U.S. Pat. No. 7,409,244 titled “Method and Apparatusfor Adjusting Interventricular Delay Based on Ventricular Pressure,” toSalo, et al., the disclosures of which are incorporated herein byreference in their entireties. In other embodiments, the lead 14 withpressure sensor 39 and/or 38 can have other suitable configurations.

The pulse generator 12 is typically implanted subcutaneously within animplantation location or pocket in the patient's chest or abdomen. Thepulse generator 12 may be any implantable medical device known in theart or later developed, for delivering an electrical therapeuticstimulus to the patient suitable for treating cardiac tachyarrhythmias.In various embodiments, the pulse generator 12 is a pacemaker, animplantable cardioverter defibrillator (ICD) or a cardiacresynchronization (CRT) device configured for bi-ventricular pacing andincluding defibrillation capabilities (i.e., a CRT-D device). While notshown in FIG. 1, the pulse generator 12 includes hardware, software, andcircuitry operable as a detection/energy delivery system configured toreceive cardiac rhythm signals from the lead electrode(s) 40, 48, 50 andpressure signals from the pressure sensor(s) 38, 39, and also to delivera therapeutic electrical stimulus to the electrodes 40, 48, 50.

In various embodiments, the CRM system 10 further includes an additionallead deployed in the right atrium 20, which lead may include one or moreadditional electrodes sensing intrinsic cardiac signals and/ordelivering electrical stimuli to the cardiac tissue within the rightatrium 20.

The pressure sensor 39 is operable to sense and to generate anelectrical signal representative of a fluid pressure parameter withinthe coronary vein 32 in which it is implanted. The pressure sensor 39can be any device, whether now known or later developed, suitable forsensing pressure parameters within the coronary venous system andgenerating and transmitting a signal indicative of such pressureparameters to another device, e.g., the pulse generator 12. In variousembodiments, the pressure sensor 39 is configured to sense and generatea signal indicative of hydrostatic pressure within the coronary vein. Invarious embodiments, the pressure sensor 39 can be amicro-electrical-mechanical system (MEMS) device, which utilizessemiconductor techniques to build microscopic mechanical structures in asubstrate made from silicon or similar materials. In variousembodiments, the pressure sensor 39 can include a micro-machinedcapacitive or piezoresistive sensor exposed to the bloodstream. Otherpressure sensor technologies, such as resistive strain gages, are knownin the art and can also be employed as a pressure sensor 39.

In other exemplary embodiments, the pressure sensor 39 can include oneor more piezoelectric elements. Such piezoelectric elements areconfigured to flex and/or deflect in response to changes in pressurewithin the coronary vein in which it is implanted, and to generate anoutput current or voltage proportional to the corresponding pressurechange. In such embodiments, the pressure sensor 39 may advantageouslybe configured to sense fluid characteristics indicative of changes incoronary venous pressure parameters, e.g., coronary venous end diastolicpressure, which in turn can be monitored over time. In addition, thepressure sensor 38 can be used to sense right atrial pressure, which canbe a useful surrogate for central venous pressure and can be monitoredover time to provide an indication of right side heart decompensation.

FIG. 2 is a schematic functional block diagram of an embodiment of theimplantable medical system 10. As shown in FIG. 2, the system 10 isdivided into functional blocks. The illustrated configuration isexemplary only, and there exist many possible configurations in whichthese functional blocks can be arranged. The example depicted in FIG. 2is one possible functional arrangement. The system 10 includes circuitryfor receiving cardiac electrical signals, coronary venous pressuresignals, and in some embodiments, right atrial pressure signals from theheart 18 and generating and delivering electrical energy in the form ofpace pulses or cardioversion/defibrillation pulses to the heart 18.

As discussed above, the cardiac lead system 13, which includes the leads14, 16 may be implanted so that the cardiac electrodes 40, 48, 50 (seeFIG. 1) contact heart tissue. The cardiac electrodes of the lead system13 sense cardiac signals associated with electrical activity of theheart. In addition, the pressure sensors 38, 39 on the lead 14 detectand generate pressure signals indicative of blood pressure within theright atrium 20 and coronary vein 32, respectively. The sensed cardiacsignals and pressure signals are transmitted to the pulse generator 12through the lead system 13. The cardiac electrodes and lead system 13may be used to deliver electrical stimulation generated by the pulsegenerator 12 to the heart to mitigate various cardiac arrhythmias. Thepulse generator 12, in combination with the cardiac electrodes and thelead system 13, may detect cardiac signals and deliver therapeuticelectrical stimulation to any of the left and right ventricles and leftand right atria, for example.

As shown, the pulse generator 12 includes circuitry encased in ahermetically sealed housing 70 suitable for implanting in a human body.Power is supplied by a battery 72 that is housed within the housing 70.In one embodiment, the pulse generator circuitry is a programmablemicroprocessor-based system, including a control system 74, sensingcircuitry 76, therapy circuitry 78, communications circuitry 80, andmemory 82. The memory 82 may be used, for example, to store programmedinstructions for various pacing and defibrillation therapy and sensingmodes, and also data associated with sensed cardiac signals or otherphysiologic data, e.g., blood pressure. The parameters and data storedin the memory 82 may be used on-board for various purposes and/ortransmitted via telemetry to an external programmer unit 84 or otherpatient-external device, as desired. In various embodiments, the storeddata can be uploaded by a clinician and/or transmitted over an advancedpatient management (APM) system, such as the LATITUDE® system marketedby Boston Scientific Corporation.

The communications circuitry 80 allows the pulse generator 12 tocommunicate with the external programmer unit 84 and/or otherpatient-external system(s). In one embodiment, the communicationscircuitry 80 and the programmer unit 84 use a wire loop antenna and aradio frequency telemetric link to receive and transmit signals and databetween the programmer 84 and communications circuitry 80. In thismanner, programming commands may be transferred to the pulse generator12 from the programmer 84 during and after implantation. In addition,stored cardiac data may be transferred to the programmer unit 84 fromthe pulse generator 12, for example.

The sensing circuitry 76 detects cardiac signals sensed at the cardiacelectrodes 40, 48, 50, as well as blood pressure signals generated bythe pressure sensors 38, 39, and signals from other implanted sensors(e.g., activity sensors providing information relating to the patient'sphysical activity and associated metabolic demand). The sensingcircuitry 76 may include, for example, amplifiers, filters, NDconverters and other signal processing circuitry. Cardiac signals andpressure signals processed by the sensing circuitry may be communicatedto the control system 74.

The therapy circuitry 78 is controlled by the control system 74 and maybe used to deliver therapeutic stimulation pulses to the heart throughone or more of the cardiac electrodes, according to a pre-establishedpacing regimen under appropriate conditions. Thus, in variousembodiments, the therapy circuitry 78 is configured to deliver pacingstimuli to the right side and, in the case of a CRT or CRT-D system suchas the CRM system 10, also to the left side of the heart 18. In variousembodiments, the therapy circuitry 78 is also configured to deliveranti-tachycardia therapy stimuli to the ventricles and/or the atria.Such therapies may include, without limitation, relatively low-energyanti-tachycardia pacing pulses as well as high-energy shocks to treatand disrupt ventricular fibrillation episodes.

The control system 74 is used to control various subsystems of the pulsegenerator 12, including the therapy circuitry 78 and the sensingcircuitry 76. The control system 74 performs various functions,including, for example, arrhythmia analysis and therapy selection. Anarrhythmia analysis section of the control system 74 may compare signalsdetected through the sensing circuitry 76 to detect or predict variouscardiac arrhythmias, and to assist selection of appropriate therapiesfor the patient. In general, the control system 74 controls therapydelivery according to pacing parameters programmed by the clinicianeither at implantation or thereafter.

As discussed above, the CRM system 10 utilizes hemodynamic performanceinformation based on the output from the implanted pressure sensors,e.g., pressure sensors 39 and/or 38, to diagnose medical conditionsincluding the onset of early decompensation resulting from CHF, andoptimizes the pacing system parameters to treat CHF-related symptoms.

In particular, as discussed in detail below, one pacing parameter thatis dynamically adjusted by the CRM system 10 to treat symptoms of earlydecompensation is the lower rate limit (LRL). The LRL is a programmedparameter defining the pacing rate (e.g., number of pulses per minute)at which the pulse generator 12 will deliver pacing stimuli in theabsence of sensed intrinsic cardiac activity. In other words, unless theCRM system 10 senses cardiac activity or metabolic demand dictatingstimulating at a different rate, the pulse generator 12 will deliverpacing stimuli at the LRL. According to various embodiments of thepresent invention, the LRL can be automatically adjusted by the controlsystem 74 upon detecting the onset of decompensation so as to cause theCRM system 10 to pace the heart at an increased rate, therebyfacilitating removal of fluid accumulated in the patient's heart and/orlungs.

As further discussed above, LVP is a useful indicator of hemodynamicperformance in patients with CHF, and can provide an indication as toworsening hemodynamic conditions, including the onset of earlydecompensation in CHF patients. In particular, the left ventricular enddiastolic pressure (LV-EDP) is an especially important measure used toevaluate hemodynamic state. That is, an increase in LV-EDP over time canbe a reliable indicator of symptoms associated with early decompensationcaused by CHF, e.g., accumulation of blood or other fluid in the heartchambers or the lungs as a result of the reduced hemodynamic performanceof the heart 18 caused by CHF.

Notwithstanding the usefulness of LVP in early decompensation detectionand treatment, obtaining direct LV pressure information chronically isboth technically and clinically challenging. As discussed in detailbelow, however, LV-EDP (or other LVP-derived parameters such as LVsystolic pressure (LV-SP), mean LVP, and LV dp/dt) can be estimatedutilizing pressure data obtained from within a coronary vein withoutrequiring direct pressure readings from the left ventricle or leftatrium. That is, in various embodiments, coronary venous pressure (CVP)is chronically sensed using implanted pressure sensors and is utilizedas a surrogate for direct LVP measurement.

Referring back to FIG. 1, the pressure sensors 38, 39 are configured todetect and generate pressure signals representative of fluid pressurewithin the right atrium 20 and the coronary vein 36, respectively. Fromthese pressure signals, pressure waveforms can be derived and evaluatedby the sensing circuitry 76 and the control system of the pulsegenerator 12. FIG. 3 illustrates pressure waveforms obtained from theright atrium (RA), left ventricle (LV), coronary sinus (CS) and variouslocations in a coronary vein (CV) in an exemplary animal study. Asshown, the coronary venous pressure (CVP) waveform takes on the samegeneral shape as the LV waveform, particularly where the CVP is takenfrom a location lower in the coronary vein, i.e., as indicated by the“Wedged” (apical two-thirds) CV pressure graph.

FIG. 4 is an illustration depicting a CVP waveform and a correspondingLVP waveform also obtained in an exemplary animal study. As can be seenin FIG. 4, the CVP and LVP waveforms correlate closely to one another.Thus, in view of the close correlation between coronary venous pressureand LV pressure, CVP can function as a surrogate for LVP in the CRMsystem 10, which can then derive one or more CVP indexes that closelycorrelate to corresponding LVP indexes, and can thus be utilized in thesame manner as the LVP indexes to adaptively adjust pacing parameters,e.g., pacing rate limits such as the lower rate limit (LRL), in responseto changes in the patient's hemodynamic status.

Thus, from FIG. 4, it can be seen that LV-EDP can be estimated based onCVP signals obtained from the pressure sensor 39 implanted in thecoronary vein 32, and optionally, the pressure sensor 38 implanted inthe right atrium (or the coronary sinus). Additionally, changes in CVend diastolic pressure (CV-EDP) over time will correlate with changes inLV-EDP. Thus, hemodynamic performance information that can be derivedfrom changes in LV-EDP over time can also be derived by monitoringchanges in CV-EDP, which as discussed above, can be directly calculatedbased on CVP signals from the implanted pressure sensors. As furtherdiscussed above, one important diagnostic application of LV-EDP changes(and thus, CV-EDP changes as well) is to detect the onset of earlydecompensation in CHF patients, which can be detected based on increasedLV-EDP caused by the accumulation of fluid in the patient's heart andlungs.

FIG. 5 is a diagram graphically illustrating an exemplary method 200 oftreating symptoms associated with CHF using the CRM system 10 accordingto one embodiment of the present invention. As shown in FIG. 5, thecontrol system 74 of the CRM system 10 monitors CV-EDP calculated fromthe output based on the output of the implanted pressure sensor 39(block 210). The control system 74 then detects changes in the CV-EDP,and in particular, increases in the CV-EDP above a programmed thresholdvalue indicative of early decompensation (block 220).

Upon detecting a CV-EDP increase above the programmed threshold, thecontrol system 74 then increases the LRL above the previously programmedvalue, thereby increasing the rate at which the heart 18 will be pacedin the absence of sensed intrinsic events (block 230). Accordingly, bypacing at the corresponding elevated rate, the CRM system 10 facilitatesremoval of blood and other fluid accumulated in the patient's heartand/or lungs, thus relieving the symptoms associated with this fluidaccumulation.

As further shown in FIG. 5, the control system 74 of the CRM system 10will continue to monitor CV-EDP during the period of elevatedpacing/heart rate resulting from the increase in LRL until one or morepredetermined events is detected (block 240). In the illustratedembodiment, upon detection of one of the predetermined events, thecontrol system 74 will return the LRL to its original settings (block250). Exemplary predetermined events that will trigger this step includethe CV-EDP returning back to a pre-established value, or alternatively,to a value equal to or below the programmed threshold value fortriggering the LRL increase. Another event that may trigger thereduction in the LRL is the passage of a prescribed time limit forpacing at the elevated rate where the CV-EDP has not fully returned to avalue below the programmed threshold. In still another embodiment, theLRL may be reduced upon a detection by the CRM system 10, based on theCV-EDP trend, of worsening hemodynamic conditions.

In various embodiments, feedback in the form of alerts or otherinformation regarding sensed events and/or CRM system 10 operatingparameters may be transmitted over an APM system to a physician or othercaregiver.

The particular CVP parameters calculated and monitored can be anyparameters useful for providing an indication of the patient'shemodynamic state, and in particular, for identifying the onset ofsymptoms associated with early decompensation. As discussed above,increases in CV-EDP provides one such useful indicator of symptoms ofearly decompensation. In various embodiments, the CRM system 10 isconfigured to calculate average CV-EDP values over predeterminedintervals, e.g., a predetermined time period or a predetermined numberof beats or cardiac cycles. For example, in one embodiment, the CRMsystem 10 generates a CVP waveform based on the CVP signal andcalculates an average CV-EDP value over a predetermined interval basedon the CVP waveform. In one embodiment, the CV-EDP value monitored is arolling average CV-EDP value, which can be monitored by the CRM system10 over time. Thus, as shown in FIG. 5, a trend in the average CV-EDPover time is monitored by the control system 74, and this trend providesthe input for triggering the LRL increase by the control system 74. Instill other embodiments, other CVP parameters may be monitored by theCRM system 10.

FIG. 6 is a flow chart illustrating a method 300 of operating the CRMsystem 10 to treat symptoms associated with CHF according to oneembodiment of the present invention. The method 300 of FIG. 6contemplates that the CRM system 10 is implanted and programmed to paceat an initial set of pacing parameters including an initial LRL. Asshown in FIG. 6, the method 300 includes acquiring a CVP signal from theimplanted pressure sensors, e.g., the pressure sensor 39 of FIG. 1(block 310). From the pressure signal, the control system 74 of the CRMsystem 10 calculates a baseline CV-EDP value (block 320). In oneembodiment, this baseline CV-EDP value may be based on a singlemeasurement at a predetermined time. Alternatively, the baseline CV-EDPvalue may be an average CV-EDP value over a predetermined samplinginterval.

As further shown in FIG. 6, the control system 74 subsequently monitorsaverage CV-EDP values (block 330), and compares the average CV-EDPvalues to the baseline CV-EDP value (block 340). Here again, the averageCV-EDP values may constitute a series of rolling average CV-EDP valueseach calculated for a predetermined time period or number ofbeats/cycles.

As shown, in comparing the average CV-EDP values to the baseline CV-EDPvalue, the control system 74 determines whether the difference (ΔCV-EDP)between at least one of the average CV-EDP values and the baselineaverage CV-EDP value exceeds a predetermined threshold amount (block350). If not, the control system 74 will continue to monitor the averageCV-EDP values and compare them to the baseline CV-EDP value. If,however, the ΔCV-EDP does exceed the predetermined threshold amount, thecontrol system 74 increases the LRL and monitors the average CV-EDPvalues at the elevated heart/pacing rates associated with the increasedLRL (block 360). In one embodiment, the CRM system 10 maintains the LRLat the increased setting for a prescribed time period, and thendetermines whether a predetermined event has occurred (block 370).

The threshold ΔCV-EDP values for triggering the LRL increase can bedetermined by the clinician at implantation or thereafter throughprogramming changes based on the patient's history and clinical needs.Additionally, the ΔCV-EDP can be based on any useful measure of CVPchanges. For example, in one embodiment, the ΔCV-EDP will be evaluatedas a change average CV-EDP value measured as a percentage of thebaseline value. Thus, in this example, the control system 74 may beprogrammed to initiate the LRL increase when the ΔCV-EDP value reaches apredetermined percentage increase over the baseline CV-EDP value, inwhich case this percentage would represent the programmed thresholdvalue described above. In another embodiment, the ΔCV-EDP may beexpressed as an absolute rise, e.g., as measured in mm/Hg, in theaverage CV-EDP over the baseline CV-EDP. In short, the CRM system 10provides for broad flexibility in defining the specific operatingparameters/thresholds.

Similar to the method 200 discussed above, exemplary predeterminedevents include the ΔCV-EDP returning to a value equal to or below theprogrammed threshold value for triggering the LRL increase. Anotherevent that may trigger the reduction in the LRL is the passage of aprescribed time limit for pacing at the elevated rate where the CV-EDPhas not fully returned to a value below the programmed threshold. Instill another embodiment, the LRL may be reduced upon a detection by theCRM system 10, based on the CV-EDP trend, of worsening hemodynamicconditions.

As shown, if one or more of the predetermined events has occurred, thecontrol system 74 returns the LRL back to its initial setting (block380). If one or more of the predetermined events has not occurred, inthe illustrated embodiment, the control system 74 further increases theLRL and continue to monitor the CV-EDP for a prescribed time period, asindicated by the return arrow to from block 370 to block 360 in FIG. 6.In another embodiment, the control system 74 will maintain the LRL atthe initial elevated rate, but will not initiate further increases inthe LRL setting (i.e., the return arrow from block 370 to block 360 inFIG. 6 is omitted).

In still other embodiments, other operating parameters may be programmedinto the control system 74 of the CRM system 10. In one exemplaryembodiment, the control system 74 may be programmed to initiate apredetermined number of LRL increases while not to exceeding a maximumpacing rate limit, e.g., the maximum sensor rate (MSR) or maximumtracking rate (MTR). Thus, for example, the control system 74 may beprogrammed to increase the LRL up to a rate setting a predeterminedmargin, e.g., expressed as a percentage of or a number of beats/minutebelow the MSR/MTR. In short, a range of operating scenarios can beimplemented according to the various embodiments of the presentinvention.

While not shown in FIG. 6, the method 300 further contemplatesrecalculating the baseline CV-EDP value(s) after completion of thetherapy cycle described above (i.e., upon returning the LRL to itsinitial programmed value). Thus, the method 300 can then be repeated asappropriate.

Thus, the CRM system 10 utilizes hemodynamic performance informationbased on the output from implanted CVP sensors to diagnose medicalconditions, such as the onset of early decompensation resulting fromCHF, and to adjust the LRL settings so as to pace the heart at anelevated rate to facilitate removal of fluid accumulated in thepatient's cardiopulmonary system as a result of CHF. The CRM system 10thus advantageously provides a means for diagnosing and treatingCHF-related symptoms based on actual patient hemodynamic stateinformation.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

We claim:
 1. A method of operating an implanted cardiac rhythmmanagement system in a patient, the method comprising: applying anelectrical stimulus to the patient's heart at a first set of pacingparameters including an LRL setting; acquiring a CVP signal from apressure sensor implanted in a coronary vein of the patient; calculatinga baseline CV-EDP value from the CVP signal corresponding to a firstinterval; monitoring average CV-EDP values over a predetermined timeinterval subsequent to the first interval; comparing each of averageCV-EDP values to the baseline CV-EDP value; determining a difference(ΔCV-EDP) between at least one of the average CV-EDP values and thebaseline average CV-EDP value automatically increasing the LRL settingin response to said difference (ΔCV-EDP) between at least one of theaverage CV-EDP values and the baseline average CV-EDP value exceeding apredetermined threshold; and subsequently automatically reducing the LRLsetting upon detecting a predetermined event.
 2. The method of claim 1wherein the predetermined event includes the ΔCV-EDP returning to belowthe predetermined threshold.
 3. The method of claim 1 wherein thepredetermined event is an expiration of a predetermined time period forapplying the electrical stimulus at the increased LRL setting.
 4. Themethod of claim 1 wherein the baseline CV-EDP value is a rolling averageCV-EDP value over a plurality of cardiac cycles or a predetermined timeinterval.
 5. The method of claim 1 further comprising recalculating thebaseline CV-EDP value after reducing the LRL setting upon detecting thepredetermined event.
 6. The method of claim 1 wherein the predeterminedthreshold is a programmed percentage change in any of the plurality ofaverage CV-EDP values relative to the baseline CV-EDP value.
 7. Themethod of claim 1 monitoring average CV-EDP values includes generating aCVP waveform based on the CVP signal and calculating an average CV-EDPvalue over a predetermined interval based on the CVP waveform.
 8. Themethod of claim 1 wherein the automatically increasing the LRL settingincludes maintaining the LRL setting at the increased setting for aprescribed time interval.
 9. The method of claim 8 further comprisingincreasing the LRL if the predetermined event is not detected after theprescribed time interval.
 10. The method of claim 9 further comprisingincreasing the LRL up to a prescribed maximum LRL if the predeterminedevent is not detected after the prescribed time interval.